Apple's latest iPhone 4S has been battling with battery drain issues. In hopes of fixing that, you can now download 5.0.1 iOS build 9A406 for iPhone 4S. Be advised that this build has only been released for iPhone 4S.
Soon after Apple started shipping iPhone 4S, early adopters started complaining about battery drain issues. A hardware issue was quickly ruled out and Apple said that a new software update would fix this problem. After a couple of weeks, Apple released iOS 5.0.1 for iPhone, iPad and iPod touch but even the new update did not prove to fix iPhone 4S battery issue. Some users actually reported that their devices started facing battery issues after they had updated to iOS 5.0.1.
Apple reached out to iPhone 4S owners and with the help of data provided by them, started working on another fix for this issue. iOS 5.1 beta 1 and beta 2 both were seeded to developers however they too weren't able to fix battery drain issues. However earlier today, Apple released iPhone 4S 5.0.1 iOS build 9A406 specifically for their latest smartphone. There are no major changes or updates in this build destined only for the iPhone 4S, but it does tackle the battery drain issue to some extent.
If you own an iPhone 4S, you can download 5.0.1 iOS build 9A406 from the direct link given below and manually restore your iPhone 4S to it. Be sure to backup your device before doing that. You can also simply connect your iPhone 4S to the computer, launch iTunes and it will automatically prompt you that a new software update is available for your iPhone 4S. It should be evident by now that this build has not been released for any other iOS-based device except the iPhone 4S.
Download iPhone 4S 5.0.1 iOS Build 9A406